Process for desulfurizing char

ABSTRACT

A process for reducing the sulfur content of char by means of a hot molten solution of cresylic acid and a caustic.

United States Patent 11 1 Robinson et a1.

1 1 PROCESS FOR DESULFURIZING CHAR [75] lnventors: Leon Robinson, Upland; Hans F.

Bauer, Diamond Bar. both of Calif 1731 Assignee: Occidental Petroleum Corporation.

Los Angcles. Calif.

[22] Filed: Sept. 27, 1973 [21] Appl. No.: 401.408

[ 1 Nov. 11, 1975 Murphy et a1. 423/461 Wenncrherg 423/461 OTHER PUBLICATIONS Mascizmtonio. P. X. The Effect of Molten Caustic on Pyritic Sulfur in Bituminous Coal. Fuel U44. pp. 269275, London.

Plillltll') Exuminer0scur R. Vcrtiz Ass/stun! EmmmerGury P. Struub AHUI'HLT. Age/1r. ur Firm-Harris, Kern, Wallen 84 Tinsley [57] ABSTRACT A process for reducing the sulfur content of chair by means of a hot molten solution of cresylic acid and :1 CllUSllC.

11 Claims, No Drawings PROCESS FOR DESULFURIZING CHAR BACKGROUND OF THE lNVENTlON Commercial desulfurization techniques only remove a portion of the sulfur present in chars. This is inadequate for purposes of complying with air purity standards which limit the amount of sulfur dioxide produced by the use of chars as a fuel. The need for a relatively sulfur-free char has therefore become very important, especially in view of dwindling supplies of oil and natural gas and abundant supplies of coal.

Conventional commercial methods for desulfurizing char generally attempt to desulfurize the carbonaceous material from which the char is manufactured, such as coal, rather than treating the char itself. Sulfur is more readily removed from coal than char because the conversion to char causes reactions between the sulfur and the inorganic and organic compounds in the coal which fixes the sulfur in the resultant char thereby making it much more difficult to remove.

One method for desulfurizing coal is by crushing and grinding the coal into fines which are introduced into a fluid medium to allow the sulfur in the form of FeS, (pyrite) to form a separate layer which is mechanically removed from the coal. This technique, however, does not remove the FeS, embedded in the uncrushed coal and does not remove any of the sulfur present in other inorganic compounds and in organic compounds.

Another method is to treat coal with hydrogen gas to leach out the sulfur by reacting therewith to form hydrogen sulfide gas. This method generally works well with coal but not with char because much of the sulfur has become fixed after the coal is converted to char and does not readily react with the hydrogen.

Hot molten caustic has also been used to leach sulfur from finely divided coal. This approach, however, only removes a relatively small portion of the sulfur and would not appear to be suitable for desulfurizing char due to the fixed condition of the sulfur therein. Furthermore, the sulfur is leached out in the molten caustic method only after the coal is in a semi fluid or plastic condition. Char does not become semi-fluid or plastic and would therefore not appear to be usable in a molten caustic system.

SUMMARY OF THE INVENTION It has been discovered that over 80% of the sulfur in coal char can be removed if the char is treated with a hot molten bath comprised of a caustic material and the cresylic acid fraction from the distillation of coal tar, hereinafter referred to as cresylic acid.

EMBODIMENT OF THE INVENTION In practicing the method of the instant invention, a caustic material is added to cresylic acid until the mixture is in a basic condition upon testing with litmus paper. The caustic may be any caustic material, such as for example, sodium hydroxide, potassium hydroxide, calcium oxide, sodium carbonate, sodium sesquicarbonate, sodium bicarbonate, or any other sodium and potassium acetate alkaline material or combination thereof.

The cresylic acid-caustic mixture as aforesaid produces an alkaline salt of the cresylic acid which is heated to a temperature which will melt the said salt and maintain it in a fluid condition. in the preferred embodiment. the mixture comprises one mole of sodium hydroxide to about one mole of cresylic acid and is heated and maintained at a temperature between about 500 to about 750F.

The ratio of char to cresylic acid-caustic mixture should be maintained at a level which will effect maximum desulfurization. In the preferred embodiment, this ratio is one part of char to at least two parts of a mixture comprising one part by weight of sodium hydroxide and three parts by weight of cresylic acid.

In the event the ratio of char to the cresylic acidcaustic mixture is less than two parts of said mixture to one part of char, at least about one part of a polyphenyl ether or a mixture thereof is preferably added thereto for each part of char to improve the contact between the char and the cresylic acid-caustic mixture. One such polyphenyl ether mixture is sold by the Mobil Oil Company under the trade name Mobiltherm."

When the char is introduced to the molten bath, it is admixed therein by means of a motor-driven stirrer or other equivalent means which will provide a thorough mixing of the char with the molten cresylic acid-caustic mixture for intimate contact therebetween. An inert medium, such as nitrogen gas, may be admixed into the mixture to eliminate the presence of oxygen therein and prevent the possibility of any reactions therewith. The elimination of oxygen from the bath, however, is not necessary to the practice of the instant invention.

The period of intimate contact between the char and the mixture of cresylic acid and caustic is referred to as the residence time and should be about two to about sixty minutes. About thirty minutes is preferred for maximum desulfurization. After the prescribed residence time, the char is allowed to rise to the surface of the bath where it is decanted or skimmed off by conventional flotation separation means. The char is thereafter washed with water to remove any inorganic residues. and then washed with organic solvents, such as acetone, to remove any organic residues.

The remaining cresylate fraction of the bath may be recovered as cresylic acid by steam distillation and recovered after the dcsulfurization is completed and preferably recycled for further use. Recycling the cresylic acid is a substantial improvement over prior methods which consumed these desulfurization reagents during the process.

The cresylic acid used in the instant invention is derived from coal tars and includes phenols, cresols, xylenols, and phenolic homologs derived therefrom. The aforesaid materials are organic acids having a thermal stability which is necessary for use in the method of the instant invention, and form alkaline salts when mixed with the caustic materials. it is believed that the alkaline salt of the cresylic acid partially solvates the char thereby rendering the char in a condition where the sulfur is leached therefrom. It is believed that the alkaline salt of any other thermally stable fatty acid, aromatic carboxylic acid or other organic acid may be substituted for cresylic acid.

EXAMPLE I 33 grams of sodium hydroxide were added to I00 grams of cresylic acid. The resultant mixture was basic to a test by litmus paper and was in a dark viscous semisolid condition. I55 grams of the semi-solid mixture was heated to 750F. under a nitrogen blanket. The solid was completely fluid at about 500F. A ZS-gram specimcn of 60 mesh char prepared from a high volatile bituminous coal was admixed to the fluid mixture and stirred for 30 minutes while the temperature was maintained at 750F. The mixture was cooled, the char was removed therefrom and washed with water to remove the inorganic residues and washed with acetone to remove organic residues. The washed specimen was thereafter dried at 212F. to remove any acetone or water and then analyzed. A second run was made on another 25-gram specimen of the same char following the same procedure as set forth above. The results were as follows:

Analysis by Weight Percent of Char Prior to Treatment with Organic Solvent-Caustic Bath:

The designation wet" in the above table refers to the analysis of the water content of the char. The designation dry" refers to the analysis of the same specimen of char discounting the presence of water and determining the weight percents of the nonaqueous constituents of the char. The above results indicate that the sulfur content of the char was reduced by about 86%.

EXAMPLE ll 50 grams of char containing 3.36% sulfur were mixed with 23.5 grams of sodium cresylate and 26.5 grams of Mobiltherm high temperature fluid. The mixture was heated to 675F. and stirred for 30 minutes. The mixture was cooled and the char removed by filtration and washed with water and acetone. The sulfur content of the char was analyzed at 0.83%, a 75% reduction.

EXAMPLE [I] 50 grams of char containing 3.36% sulfur were mixed with 44.1 grams of sodium cresylate and 55.9 grams of Mobiltherm high temperature fluid. The mixture was heated to 675F. and stirred for 30 minutes. After washing the char sulfur content was 1.2%, a 64% reduction.

While the embodiment of the invention chosen herein for purposes of the disclosure is at present considered to be preferred, it is to be understood that this invention is intended to cover all changes and modifications in the disclosed embodiments which fall within the spirit and scope of the invention.

What we claim as our invention is:

l. A process for reducing the sulfur content of char comprising the steps of:

a. admixing char with a basic molten bath comprising an alkaline salt formed from 1. an organic acid comprising the cresylic acid fraction from the distillation of coal tar, and

2. a caustic material selected from the group consisting of alkali metal. and alkaline earth metal, oxides, hydroxides, carbonates, acetates or mixture thereof, wherein the ratio of the moles of said caustic material to the moles of said cresylic acid is greater than about one;

b. maintaining said bath in a molten condition until sulfur in the char is leached therefrom. and

c. separating said char of reduced sulfur content from the molten bath.

2. The process as set forth in claim I wherein said char is coal char and said caustic material is a alkali metal hydroxide.

3. The process as set forth in claim 2 wherein said hydroxide is principally sodium hydroxide, said char has a residence time in said bath of about 2 to 60 minutes, and said bath is at a temperature of about 500 to about 750F.

4. The process as set forth in claim 3 wherein said bath is steam distilled following following the reduction of the sulfur content of said char to recover said cresylic acid fraction therefrom and recycling said cresylic acid fraction for further use in said process.

5. The process as set forth in claim 3 wherein said char has a residence time in said bath of about thirty minutes.

6. The process as set forth in claim 2 wherein at least two parts of said bath is provided for every part of char in said bath.

7. The process as set forth in claim 2 wherein said bath comprises about one mole of said hydroxide to about one mole of said cresylic acid fraction.

8. The process as set forth in claim 2 wherein about one part of a polyphenol ether or a mixture of polyphenol ethers is admixed with said bath for every part by weight of char in said bath.

9. The process as set forth in claim 1 wherein said organic acid has a high thermal stability and contains phenol, cresols, xylenols, or phenol homologs derived therefrom.

10. A process for reducing the sulfur content of coal char comprising the steps of:

a. admixing coal char with a basic molten bath comprising an alkaline salt formed from 1. the cresylic acid fraction from the distillation of coal tar, and

2. a hydroxide of an alkali metal wherein the ratio of the moles of said hydroxide of an alkali metal to the moles of said cresylic acid is about one.

b. maintaining said char in said basic molten bath until sulfur in the char is leached therefrom, and

c. separating the char of reduced sulfur content from the basic molten bath.

11. The process as set in claim 10 wherein said hydroxide is principally sodium hydroxide, said coal char is maintained in said basic molten bath for a residence time of from about 2 minutes to about 60 minutes, and said basic molten bath is at a temperature of about 500 to about 750F.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,919,118 DATED z-November 11, 1975 INVENTOR(S) Leon Robinson and Hans F. Bauer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 4, -F.-- should be inserted after "500"" Column 4, line 19, (claim 3) --F.-- should be inserted after "500" Column 4, line 60, --F.-- should be inserted after "500" In two occurrence Column 4, lines 36 and 37 change "nolyphenol" to nolyphenyl Signcd and Scaled this sixth D y of April 1976 A ttesr:

RUTH C. MASON C. MA Arresting Office, RSHALL DANN ummissioner ujlalenrs and Trademarks 

1. A PROCESS FOR REDUCING THE SULFUR CONTENT OF CHAR COMPRISING THE STEPS OF: A. ADMIXING CHAR WITH A BASIC MOLTEN BATH COMPRISING AN ALKALINE SALT FORMED FROM
 1. AN ORGANIC ACID COMPRISING THE CRESYLIC ACID FRACTION FROM THE DISTILLATION OF COAL TAR, AND
 2. A CAUSTIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL, AND ALKALINE EARTH METAL, OXIDES, HYDROXIDES, CARBONATES, ACETATES OR MIXTURE THEREOF, WHEREIN THE RATIO OF THE MOLES OF SAID CAUSTIC MATERIAL TO THE MOLES OF SAID CRESYLIC ACID IS GREATER THAN ABOUT ONE, B. MAINTAINING SAID BATH IN A MOLTEN CONDITION UNTIL SULFUR IN THE CHAR IS LEACHED THEREFROM, AND C. SEPARATING SAID CHAR OF REDUCED SULFUR CONTENT FROM THE MOLTEN BATH.
 2. a caustic material selected from the group consisting of alkali metal, and alkaline earth metal, oxides, hydroxides, carbonates, acetates or mixture thereof, wherein the ratio of the moles of said caustic material to the moles of said cresylic acid is greater than about one; b. maintaining said bath in a molten condition until sulfur in the char is leached therefrom, and c. separating said char of reduced sulfur content from the molten bath.
 2. The process as set forth in claim 1 wherein said char is coal char and said caustic material is a alkali metal hydroxide.
 2. a hydroxide of an alkali metal wherein the ratio of the moles of said hydroxide of an alkali metal to the moles of said cresylic acid is about one, b. maintaining said char in said basic molten bath until sulfur in the char is leached therefrom, and c. separating the char of reduced sulfur content from the basic molten bath.
 3. The process as set forth in claim 2 wherein said hydroxide is principally sodium hydroxide, said char has a residence time in said bath of about 2 to 60 minutes, and said bath is at a temperature of about 500* to about 750*F.
 4. The process as set forth in claim 3 wherein said bath is steam distilled following following the reduction of the sulfur content of said char to recover said cresylic acid fraction therefrom and recycling said cresylic acid fraction for further use in said process.
 5. The process as set Forth in claim 3 wherein said char has a residence time in said bath of about thirty minutes.
 6. The process as set forth in claim 2 wherein at least two parts of said bath is provided for every part of char in said bath.
 7. The process as set forth in claim 2 wherein said bath comprises about one mole of said hydroxide to about one mole of said cresylic acid fraction.
 8. The process as set forth in claim 2 wherein about one part of a polyphenol ether or a mixture of polyphenol ethers is admixed with said bath for every part by weight of char in said bath.
 9. The process as set forth in claim 1 wherein said organic acid has a high thermal stability and contains phenol, cresols, xylenols, or phenol homologs derived therefrom.
 10. A process for reducing the sulfur content of coal char comprising the steps of: a. admixing coal char with a basic molten bath comprising an alkaline salt formed from
 11. The process as set in claim 10 wherein said hydroxide is principally sodium hydroxide, said coal char is maintained in said basic molten bath for a residence time of from about 2 minutes to about 60 minutes, and said basic molten bath is at a temperature of about 500* to about 750*F. 